Web tensioning device



MarchZl, 1967 J. BQLITTLE WEB TENSIONING DEVICE 3 Sheets-Shree?l 1 Filed May 27, 1965 INVENTOR. JOHN B. LITTLE AGENT March 21, 1967 3 Sheets-Sheet 2 Filed May 27, 1965 March 21, 1967 J. B. LITTLE WEB TENsIoNING DEVICE s sheets-sheet s Filed May 27, 1965 United States Patent O 3,310,062 WEB TENSIONING DEVICE John B. Little, Chappaqua, N.Y., assignor to International Business Machines Corporation, Armonk, N.Y., a corporation of New York Filed May 27, 1965, Ser. No. 459,269

13 Claims. (Cl. 134-64) This invention relates to web feeding and more particularly to an apparatus for tensioning a web in a continuous multi-bath wet treatment web processing apparatus.

The prevention of damage to the surface of a web which is being processed through a succession of processing tanks can be a particularly vexing problem. Not only does the wet processing soften the coating of the web so `as to ren-der it more vulnerable to injury, but also the very geometry of the web path necessitates that some form of positive restraint be applied to opposite surfaces of the continuous web, to guide it into and out of the successive processing tanks. If extra'material is present at the edges of the web, such as the marginal sprocket holes in a motion picture film, edge Contact guides may be employed without fear of damage to the web coating. As the web becomes wider and thinner, the eiciency of edge guidance diminishes, and in the limit, edge guidance fails entirely. When such happens, other expedients must be employed. Rollers, however smooth, will frequently damage Va web coating.` Providing the rollers with a gaseous or liquid insulating film (fluid bearing) helps toward alleviating the danger of scratching. It, however, raises other problems which can also be troublesome. Fluid bearings usually employ small flow passages, and therefore, require a iluid which is free from contaminants which would tend to clog the passages. Fluid bearings, while acting as servo devices, arey extremely complex to balance in a long continuous web process, and delterious dynamic oscillation, or hunting, frequently arises in the system, particularly lwhere Wide variations may occur in the system parameters.

The present invention seeks to overcome the problem of web Asurface damage by employing the processing fluid itself as a sort of liquid roller. The liquid weights the loop, or bight, in the processing tank, and at the same time provides a servo-type of action which exploits the inherent damping characteristics of the liquid itself to provide a web tensioning device that will operate stably over a wide range of system parameters.

In its simplest form, the invention forms a loop in the web between two rollers which contact the reverse, or non-emulsion, side of the web. The loop is permitted to sag into the processing tank between two side plates, or baffles, which are separated by the width of the web. The web loop together with the bafes form a sort of chamber into which the processing uid is continuously pumped. If the rate of injection is greater than the losses of fluid around the edges of the web, the loop will fill with iiuid and grow heavier. As it grows heavier, it will sag to a position whereiny the bottom of the loop extends bef yond the bottom edge of the bafes, thus creating an increased leakage. If the leakage 'exceeds the influx of fluid the loop will rise to adjust the elux to the influx, and the system will stabilize at a point wherein the weight of entrapped fluid equals twice the web tension. If the web tension increases, the quantity of iluid will increase, and conversely. If the flow of fluid changes, the web loop will change its position to adjust the leakage to the How of fluid in. By suitable design and adjustment of the baflles and surrounding fluid containers, the system may be made self-damping for wide variations in system parameters,

3,310,062 Patented Mar. 21, 1967 ICC of protecting the web surface against scratching damage. It is, therefore, an object of this invention to provide 'a web tensioning apparatus by entrapping a volume of fluid within a loop formed in the web and introducing Y liquid thereinto to equal the flow of liquid lost.

A further object of the invention is to provide a web tensionuing device for a wet processing system which employs the weight of the processing fluid entrapped in a loop of the web as a form of Huid tensioning roller.

Yet another object is to provide a web tensioning device by forming a loop in the web between two side plates spaced apart a distance equal to the width of the web and introducing liquid into the chamber formed by the loop and the side plates.

An even further object is to provide a web tensioning device by forming a loop in the web between two side plates spaced apart a distance equal to the width of the web introducing liquid into the chamber formed by the loop and the side plates and forming the side plates so as to provide an exit orifice for the flow of fluid out of the chamber which is a predetermined function of the length of the loop in the web.

The foregoing and other objects, features and advantages of the invention will be apparent from the following more particular description of a preferred embodiment of the invention, as illustrated in the accompanying drawings: f

In the drawings: ,A

FIG. 1 shows a typical wet processing apparatus in which the invention can be most advantageously prac-` ticed.

FIG. 2 is a sectional perspective view of onevof the .tanks of FIG. 1.

FIG. 3 is a section taken along the line 3-3 of FIG. 4 showing an alternative structure for adjusting the water level.

FIG. 4 is a plan view looking down into the tank. FIG. 5 shows an alternative shape of the liquid retaining baffles. Y

FIG. 6 shows an alternative shape of the liquid retaining baffles.

FIG. 1 represents a typical continuous multi-bath wet processing apparatus wherein a web 10 is fed under slight tension from a supply roll 5, passed successively through a progression of processing tanks 20, and finally Wound on a take-up roll 6. Each of the tanks 20 is identical in while at the same time preserving the desirable feature its physical construction, but employs a different processing iiuid in accordance with the dictates of the process. If, for example, the web 10 were an exposed photographic film, the tank 20-1 would contain the developing solution, v20-2 the wash water and stop bath, and tank 20-3 the hypo or fixer. Obviously, a drier would be interposed between the final tank 20-3 and the tank-up reel 6. The rate of feed would be adjusted to provide the requisite processing -time in each bath.

As soon as the web 1,0 enters the first tank 20-1 and is wet by the solution therein, it becomes vulnerable to damage. The upper surface 10A, the surface to be procf essed, ,must, therefore, be protected against abrasion. The bottom surface 10B need not be protected. It may, therefore, be guided over ordinary rollers.

Before examining the detailed structure of the process-y ment of a member through a liquid produces a viscous drag, this force will add to the friction forces, and will infact exceed them. Not only does this increase the reeling force, but also it causes the web tension to be non-uniformly distributedl throughout the web length. The tension between reel 5 and tank 20-1 will be the drag imposed. by reel 5. The tension between tanks 20-1 and 20-2 will add the friction and viscous drag of the rst tank.` Each successive tank will add its drag, so that the tension at the take-up reel 5 will be maximum. Each processing tank, therefor-e, as will be explained, in addition to being adjustable is self-servoing to compensate automatically for this distribution of forces.

If a weight is supported by two lines, the tension in the lin'es is equal to half the weight. If a roller is supported by a web, the web tension is equal to one half the weight. If the web is moving at constant speed, the web tension (neglecting friction) is unchanged. Friction, accelerating forces, and viscous drag merely increase the tension on the output side of the system. Since the instant invention forms in essence a liquid roller, it can be said that, as a first approximation, the weight of the liquid entrapped in the bight of the web must equal twice the web tension. Friction and viscous drag merely modify the relationship to the extent of providing that the weight of entrapped uid will equal the sum of the tensions in the input and output sections of the web.

A further phenomenon is that of dynamic oscillations. When webs up to two feet in width and only several thou-sandths of an inch in thickness are fed through a succession of tanks, non-uniformity in the elasticity of the web can induce transient perturbations in the system, which, if unrestrained, could cause destructive oscillations. Since liquids areincompressible and viscous, they have inherently good damping characteristics. Any tendency therefore, to develop oscillations in the web 1t) will be resisted and damped by the processing uid. The adjustments on each tank provide separate control at each station to optimize the servo action and the damping.

Returning now to the apparatus, the web is guided into and out of each of the tanks over rolls 21 and 22 which contact the underside 10B of the web. The liquid roller forms a loop, or bight, 10C in each of the tanks. The tanks consist of an outer tank 23, having an overflow pipe 24, and an inner tank 30 to which the rollers 21 and 22 are rotatably fastened. The inner tank '30 with its rollers 21 and 22 is fixed so as to preserve the line of feed between the reels 5 and 6. The outer tank 23 is mounted for vertical movement relative to the inner tank 30 by means of a jackscrew structure 2S, orv other height adjusting means. Processing fluid is sprayed upon the inner surface (upper surface 10A)l of the web loop 10C by spray nozzles and feedpipes 26 and 27 (27 lies behind 26 in FIG. 1). The processing fluid, thus introduced, fills the outer tank 23 to the level of the overflow pipe 24 from whih it is collected, ltered, reactivated, replenished (as the process requires), and recirculated by a pump to the nozzles 26 and 27,.

The inner tank 30 (see FIG. 2) is actual-ly a shell, at the top and the bottom, and is immersed in the outer tank 23. This shell consists of identical front and rear walls 31 and 32 and side walls 33 and 34 joined so as to have a rectangular cross section. Extensions 31A, 32A, 31B, and 32B of the front and rear walls 31 and 3 2 journal the rollers 21 and 22. The front and rear walls 31 and 32 are cut away from the bottom edge upward in generally V-shaped cutouts 31C and 32C. These inverted weirs operate to provide variable orifices through which the liquid which is entrapped in the loop 10C of the web may escape into the outer tank 30. These weirs may be simple V cutouts or may have a parabolic or hyperbolic shape as shown.

With the construction above-described, processing liquid sprayed through nozzles 26 and 27 impinges on the active surface 10A of the web loop 10C and is entrapped between the front and rear walls 31 and 32, which are spaced apart a distance slightly greater than the width of the web 10. As the volume of liquid is increased in the web loop, the loop will be weighted to sink deeper into the tank 30. As soon as the bottom of the tape loop sinks beneath the apex of the Weir-like openings 31C and 32C, the entrapped liquid will begin to escape. The tape loop will continue to sink deeper until a sufficient area of the weirs is exposed to permit an escape of liquid just equal to ilow of iiuid into the loop, minus of course any leakage of fluid between the web edges and the abutting front and rear walls 31 and 32. At this position the weight of the entrapped fluid will equal the sum of tensions in the two -legs of the loop.

If, for any reason, the web tension should increase, the loop 10C will be drawn upward, thus restricting the efflux of fluid through the weirs, and liquid will accumulate in the loop 10C. When the Weight of entrapped liquid equals the new web tension, the reduced exposed escape path will be less than that necessary to exhaust a ow of liquid equal to the influx. The web loop, will, therefore, sink deeper into the inner tank to restore the former orice area.

If the web tension should decrease, the excess weight of entrapped liquid will produce a larger loop to expose a greater weir area and increase the efux of liquid. When sufficient liquid is spilled to balance the weight of entrapped fluid with the web tension, the excess spillage will continue to lighten the iluid roller and the `loop will move upward to its original position where the efux equals the inux of liquid.

If the influx through nozzles 26 and 27 increases, so that the influx exceeds the etiiux, the weight of entrapped uid will increase to enlarge the loop 10C to expose more weir area. This increases the efflux, and stability will be achieved when the loop exposes a sufficiently greater weir area to compensate for the increased influx.

For a diminution of the influx, the now greater elux will lessen the weight of entrapped fluid causing the loop to shrink. When the loop shrinks to a position wherein the exposed weir area permits an efux equal to the new diminished input flow, the system will stabilize.

In all of the preceding examples of increased and de-J creased web tension, and increased and decreased input flow, the resulting changes in the web position and output flow do not occur sequentially, but simultaneously. Since none of the system perturbations can occur instantaneously, these changes occur smoothly, and follow the changes in the input parameters with little delay. The construction, therefore, operates as a true servo. Each change in an input parameter results in an unbalance of forces which operates to restore the system balance.- Briefly stated, an increase in web tension results, after balance is restored, in a greater volume of entrapped fluid with the same web loop position. An increase in fluid input, with constant web tension, results in a longer loop, and thus an increased eiilux, but the same volume of entrapped fluid.

The highly over-simplified explanation just proffered, while valid in essence, needs considerable amplification in order to explain the operation when the outer tank with its liquid level is brought into coaction with the inner tank 30 and its weirs 31C and 32C. The level of liquid, the water table, in the outer tank 23 is xed in that tank by the -overow pipe 24. By adjustment of jack 25, the tank 23 and the water table may be raised or lowered with respect to the inner tank 30, its weirs 31C and 32C, the web loop 10C, and the uid it entraps. Whereas, with a lowered water table, the web tensioning force is equal to the weight of the entrapped liquid, as soon as the water table rises above the bottom of the web loop, it begins to provide a buoying force thereto. The web tensioning force nowbecomes the weight Vof the entrapped fluid above the Waterl table. This is the head of the entrapped tluid, and will continue to be a function of the web tension. The total volume of entrapped fluid will, however, now be a function of the web tension, the water table height, and the rate of flow into the loop. Since the weir openings will now be partially, or even completely, immersed in the Water table the discharge through weirs will be into air and into the water table. Obviously, the discharge into air will occur more freely than the discharge into the water table. Thus, by adjustment of the water table height, it becomes possible to adjust the effective discharge c-onfiguration ofthe Weirs.

An ancillary benefit of adjusting the water table height is derived from the fact that the immersion of the web in the processing fiuid effects a viscous damping thereon. By virtue of the mass of the liquid, it will resist any tendency of the webto. fiutter, thus damping any oscillations.

As previously stated, each successive processing station adds its viscous drag and friction to increase the web tension. Thus, the tenion a the take-up reel 6 (FIG. 1) is greatest. To adjust for this tension the servo-action in the tank 20-3 yields a higher head of liquid therein than in the preceding tank 20-2. The tank 20-2 in turn selfadjusts with a higher liquid head than the first tank 20-1in the series. Although the jack adjustments have been shown progressing from lowest at 20-3` to highest at 20-1, this need not necessarily obtain. If, for example, the process requires that one of the tanks Vhave a very rapid fluid circulation rate, then that tank would require a substantially different adjustment t-o damp the system properly.

Without attempting to define the interplay of dynamic forces mathematically, if such can be done with meaningful definition, it will be appreciated that the inherent fiexibility of the system will accommodate a wide variety of processing speeds, flow rates, 'and variations in web characteristics. The self-servoing construction, together with the dam-ping of the liquid medium will automatically adjust for wide variations in the system parameters. Additional compensation is provided by the manual adjustment of the water table and discharge opening configuration.

Turning now to FIGS. 3 and 4 which show an alternativestructure for adjusting the water table height, one can gain a better insight into the construction of the tanks, for, except for the standpipe construction the structure is similar to -the other embodiments. In FIG. 4, the disposition of the spray nozzle 26 and 27 to cover the width of the Web is illustrated more graphically. For a wider web, spray nozzles would be added -to cover the web. So also can the escape of entrapped iiuid from the loop through the weirs into the outer tank be seen. The Water table height adjustment in these figures consists of a star1dpipe 28 which is adjustably slideable in a liquid-tight gland 29 in the bottom of the outer tank 23, which is now fixed. Thus, by loosening the packing gland 29 and sliding the standpipe 29 therein, the water table height may be adjusted to any desired level.

While there are no exact mathematical guideposts for determining the configuration of the discharge ports for the entrapped liquid, it will readily be appreciated that forms other than the inverted V-shaped construction of FIGS. 1 through 4 may be employed. FIG. 5 represents one modification which might be characterized as having maximum dynamic stiffness. By that, it is meant that for small changes in web loop configuration a maximum change in the discharge area is effected. Specifically, the inner tank 30 is a simple openended shell with no cutouts in the front and rear walls 31 and 32. The tape loop 10C must now sink below the straight lower edge of the front and rear walls to provide a discharge opening. Intuitively, one can appreciate that the rate of change of the area of the discharge opening with respect to loop size is greater than that in the V configuration. Thus, a stiffer system results. In FIG. 5, the discharge opening is a circular segment defined by the straight lower edge of the inner tank and the circular (or possibly catenary) shape 6 of the .bottom of the tape loop. While this discharge is shown as occurring under the water table, by suitable adjustment of the water table level, this discharge may occur totally into air or partially into both.

Another possible embodiment, which is a compromise between the square-edge of FIG. 5 and the V of FIGS. 1-4 is shown in FIG. 6. This might be characterized as a step function which approximates the inverted V, but is achieved by means of the holes 35, which are drilled through the front and rear Wall 31 and 32 of the inner tank 30. It will be noted that the pattern of these holes is pyramidal so that as the tape sinks deeper, the rate of change of flow increases, much in the manner of the inverted V Weir. These holes 35, in addition to having the pattern shown, may vary in size to effect a non-uniform distribution. The other features of adjustable water table, either as shown, or with the standpipe arrangement remain the same for the modification of FIG. 6.

While it has not been shown, it is worthy of mentioning in passing, that the discharge openings in any one of the modifications illustrated may be made adjustable by securing gates to the outside of the inner tanks 30 to vary the configuration of the discharge openings. These need l be nothing more than simple slotted plates secured by wingnuts to the outsides of Walls 31 and 32. In FIG. 5, for example, the adjustable gates would extend below the lower edge to change the shape thereof from a straight edge to the desired configuration. In FIG. 6 selected ones of the holes 35 could be blocked. In the remaining figures the curve of the Weir would be modified by the sliding gates. The optimum shapes are preferably obtained by trial and error for each separate combinationof system parameters to achieve the maximum servo efficiency together with the necessary critical damping.

From the foregoing description, it will be seen that a liquid roller web tensioning apparatus has been provided, wherein the processing liquid is entrapped between walls abutting the sides of a loop in the web. The web loop automatically adjusts to regulate the eliiux of iiuid to the infiux, and the head of entrapped fiuid automatically adjusts to yoffset the web tension.V Thus, a self-servoing web tensioning device is provided which tensions the web, with the only contact therewith being the liquid employed in the process.

While the invention has been particularly shown and described ywith reference to a preferred embodiment thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention.

' What is claimed is:

1. A web tensioning apparatus comprising:

(a) means for guiding the web to form a freely hanging pendulous loop therein;

(b) a pair of walled members straddling the edges of the web, coextensive with the loop therein, and spaced apart a distance equal to the Width of the web to form, together with the web, a liquid-retaining chamber;

(c) and mean-s for inducing a continuous flow of liquid into the chamber formed by said walled members and said loops;

whereby ya volume of liquid will be entrapped in said chamber to tension the web,v and the loop will automatically sag under the weight of the entrapped liquid to a position beneath the said walled members wherein the openings thus produced will provide an efflux of liquid from sai-d chamber equal to the fiow of liquid induced thereinto.

2. Apparatus for restraining a web-like member to form a pendulous loop comprising:

(a) a pair of parallel spaced rollers over which the web passes and between which the web sags to form a freely hanging loop;

(b) a pair of walled members straddling the loop to form together with the loop a liquid-retaining chamber', the said walled members having inverted generally V-shaped cutouts extending upwardly from the bottom edges thereof to provide openings out of said chamber whose cross-sectional areas are determined by the length of the loop,

(c') and means for inducing a continuous flow of liquid into the said chamber.

3. A liquid servo apparatus for controllably maintaining a pendulous loop in a web which is subjected to varying tension comprising:

(a) a pair of parallel spaced walled members, spaced apart a distance equal to the width of the web in which the loop is to be maintained;

(b) a pair of rollers supporting the web to feed between said walled members and to permit the formation of a loop in the web which together with the walled members forms a liquid retaining chamber;

(c) means for inducing a constant flow of liquid into the chamber formed by the loop and the walled members, whereby liquid becomes entrapped therein to balance the web tension;

'(d) an outer tank surrounding said loop and said walled members, and having means for adjusting the liquid level therein relative to said Walled members and said loop;

whereby the volume of the liquid entrapped in said chamber will automatically adjust so that its weight will equal the web tension force, and the loop size will automatically adjust to provide an elux of liquid equ-al to the influx.

4. The apparatus of claim 3 wherein said walled members are provided with inverted generally V-sha-ped cutouts extending upwardly from the bottom edges, to provide openings out of said chamber whose cross-sectional areas are a function of the loop leng-th.

5. The `apparatus of `claim 3 wherein said Walled members are provided with holes which are successively uncovered as the loop increases in size to thereby provide exit passages for the entrapped liquid having a total larea which increases as the loop size increases.

6. The apparatus of claim 3 wherein said walled members have a straight bottom edge beneath which the web loop sags to form the variable area discharge opening for the entrapped liquid from said chamber.

'7. The apparatus of claim 3 wherein the means for adjusting the liquid level relative to said walled members and said loop comprises means for adjustably moving the outer tank relative to the w-alled members, and the outer tank has an overflow pipe iat a xed level in the tank.

8. The .apparatus of claim 3 wherein the means for adjusting the liquid level comprises a standpipe in the outer tank and means for adjustably -altering the height of the standpipe within the outer tank.

9. In a web processing apparatus including a supply reel, a take-up reel, a succession of wet processing stations for chemically operating upon the web, and means forv feeding the web under tension through the successive baths, means for guiding the feeding of the web through each of the processing stations, comprising:

(a) an outer tank having means for maintaining a predetermined level of liquid therein;

(b) lan inner shell disposed within said outer tank and having a pair of spaced side walls, spaced apart a distance equal to the width of the web, the bottom edge of said walls being spaced above the bottom of said outer tank;

(c) a pair of rollers disposed transversely of the web above said tank and said side walls supporting the underside of said web, and spaced apart a distance to permit the formation of a pendulous loop in said web, which together with said side walls forms a liquid retaining chamber;

(d) means for inducing a constant oW of processing liquid between said side walls and into the loop in said web to entrap a weight of liquid in said chamber and thus weight the loop;

whereby the loop in said web will accumulate a weight of entrapped liquid to balance the web tension forces, and the web loop will automaticaly adjust its length to provide a discharge opening for the entrapped liquid which will pnovide an etllux of liquid from said loop into said outer tank equal to the flow liquid induced into said loop.

lll. The apparatus of claim 9 wherein the spaced side walls of said inner shell are provided with inverted generally V-shaped cutouts extending upwardly from the bottom edges, to provide openings out of said chamber varying in cross-section configuration as a function of the loop length.

11. The apparatus of claim 3 wherein the spaced side walls of said inner shell are provided with inverted generally V-shaped cutouts extending upwardly from the bottom edges, to provide openings out of said chamber varying in cross-section configuration las a function of the loop length.

l2. The apparatus of claim 9 wherein the outer tank has a constant level of liquid therein and is vertically adjustable with respect to said inner shell.

13. The apparatus of claim 9 wherein the outer tank has a standpipe therein, together with means for adjusting the extension of the standpipe within the tank, to vary the level of liquid therein.

No references cited.

CHARLES A. WILLM-UTH, Primary Examiner.

R. BLEUTGE, Assistant Examiner. 

1. A WEB TENSIONING APPARATUS COMPRISING: (A) MEANS FOR GUIDING THE WEB TO FORM A FREELY HANGING PENDULOUS LOOP THEREIN; (B) A PAIR OF WALLED MEMBERS STRADDLING THE EDGES OF THE WEB, COEXTENSIVE WITH THE LOOP THEREIN, AND SPACED APART A DISTANCE EQUAL TO THE WIDTH OF THE WEB TO FORM, TOGETHER WITH THE WEB, A LIQUID-RETAINING CHAMBER; (C) AND MEANS FOR INDUCING A CONTINUOUS FLOW OF LIQUID INTO THE CHAMBER FORMED BY SAID WALLED MEMBERS AND SAID LOOPS; WHEREBY A VOLUME OF LIQUID WILL BE ENTRAPPED IN SAID CHAMBER TO TENSION THE WEB, AND THE LOOP WILL AUTOMATICALLY SAG UNDER THE WEIGHT OF THE ENTRAPPED LIQUID TO A POSITION BENEATH THE SAID WALLED MEMBERS WHEREIN THE OPENINGS THUS PRODUCED WILL PROVIDE AN EFFLUX OF LIQUID FROM SAID CHAMBER EQUAL TO THE FLOW OF LIQUID INDUCED THEREINTO. 